Typical radionuclides used for neutron detection are 3He (helium-3), 6Li (lithium-6), 10B (boron-10), 155,157Gd (Gadolinium-155,157), and etc. Among them, 3He has the best comprehensive performance, but it is seriously undersupplied and expensive, and a substitute for 3He is accordingly being explored in the world. In summary, 10B is a better choice at present. As neutron sensitive material, however, 10B. 10B compounds or mixtures containing 10B in solid must be adhered to the surface of the detector structure in a thin film in order to effectively play a role of the neutron detection, especially when they are applied to the common proportional gas detectors for neutron detection. When solid 10B, 10B compounds or mixtures containing 10B as neutron sensitive materials are used in common proportional gas detectors for neutron detection, the sensitive film need to satisfy with the following requirements: the film is uniform; the thickness is appropriate (generally about 1-5 microns); and the amount of other isotopes, other elements or compounds is as low as possible.
There are many methods to form sensitive films on surfaces of neutron detectors, such as chemical vapor deposition, physical vapor deposition (including magnetron sputtering and electron beam evaporation), electrostatic spraying, thermal diffusion, and the latest atomic film deposition. Chemical vapor deposition, which involves large amounts of chemical pollution, safety protection and waste disposal, is rarely used. WO2014120295A2 discloses a sensitive film formed by magnetron sputtering in which a thinner and more compact film is formed; but the sputtering equipment is expensive, the target material is much more lost, and the sputtering time is long. CN101314842A discloses a sensitive film formed by electron beam evaporation, such film has a similar advantages or disadvantages to the film formed by magnetron sputtering. US2013062531A1 discloses a sensitive film formed by electrostatic spraying in which the film is formed very quickly; but there are some potential problems such as large air gap of sensitive film, and poor control of total amount and uniformity. CN102967875A discloses a sensitive film formed by thermal diffusion which is smooth and steady in forming the film; but the overall efficiency is often low because the neutron-sensitive elements are fused and embedded in the detector wall material which brings about an increase in the proportion of ineffective components. CN103160799A discloses a sensitive film formed by atomic film deposition in which a film with the highest uniformity and compactness is formed; however a variety of gas components is required to participate in the reaction, and the formation of a large-scale film is slower and more expensive.